I disagree, and many other owners will too!
I believe it is fine to leave a chameleon in a large enclosure from baby-adult.The main issue of having such a large enclosure for a small chameleon is the feeding - but if he is cup-fed there shouldn't be a problem.
I'm getting my first chameleon in a few weeks, and I have asked this question in another thread and other members said the same thing.
Look at it this way; in the wild, they are born in a huge rainforest - not put in small enclosures.
Many times we forget where our pets came from!
If you have the money to buy smaller enclosures then go for it - but I see nothing wrong as long as you closely watch your guy in a large enclosure for his life.